In one of those messages recently, a woman said her insurer denied free coverage for the NuvaRing. This small plastic device, which is inserted into the vagina, works for three weeks at a time by releasing hormones similar to those used by birth control pills. She said her insurer told her she would be responsible for her contraceptive expenses unless she chooses an oral generic birth control pill. The NuvaRing costs between $15 and $80 a month, according to Planned Parenthood.

In addition, the federal government has given plans some flexibility by allowing them to use “reasonable medical management techniques” to keep their costs under control. So if there is both a generic and a brand-name version of a birth-control pill available, for example, a plan could decide to cover only the generic version without cost to the patient.

As for the NuvaRing, even though they may use the same hormones, the pill and the ring are different methods of birth control. As an official from the federal Department of Health and Human Services said in an email, “The pill, the ring and the patch are different types of hormonal methods … It is not permissible to cover only the pill, but not the ring or the patch.”

Guidance from the federal government clearly states that the full range of FDA-approved methods of birth control must be covered as a preventive benefit without cost sharing. That includes birth control pills, the ring or patch, intrauterine devices and sterilization, among others.

But despite federal guidance, “we’ve seen this happen, plenty,” says Adam Sonfield, a senior public policy associate at the Guttmacher Institute, a reproductive health research and education organization. “Clearly insurance companies think things are ambiguous enough that they can get away with it.”

If you are denied coverage, your defense is to appeal the decision, and get your state insurance department involved.

“The state has the right and responsibility to enforce this law,” says Sonfield.